The present invention relates to the graphical display of data. More specifically, the invention relates to the display of chromatographic separation data that are a series of measurements over time in a graphical format, e.g., as a series of bands.
Analysis of biological samples often requires the resolution and characterization of the constituent elements of the sample. The more interesting of these constituents are macromolecular structures, e.g., proteins, nucleic acids, carbohydrates, and the like. Typically, analytical separation of macromolecular species is carried out using chromatographic techniques. Of particular widespread use are electrophoretic techniques that employ slab-gels disposed between two glass plates as a separation matrix. Samples containing the macromolecular species that are sought to be analyzed, are introduced into wells at one end of the slab gel. An electric current is then applied through the gel drawing the macromolecular species through the gel by virtue of a charge either on, or otherwise associated with the macromolecular species. Each sample travels through the gel substantially linearly, e.g., in a lane corresponding to its well.
As the sample progresses through the gel, molecules of different size and/or charge will have different mobilities through the gel, and will separate into bands that reflect their relative size and/or charge. Upon completion, the gel is stained or otherwise examined whereby the various bands can be visualized and compared with standard macromolecular compounds, e.g., having standard molecular weight and/or charge, e.g., isolectric point.
For example, in the case of protein analysis using sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE), proteins are drawn through the gel matrix in a highly charged detergent micelle (SDS) to ensure that the proteins, regardless of charge, will electrophorese through the gel. The proteins will travel at a rate that is proportional to their size. Once separated, the protein bands are stained, e.g., with coomassie blue or silver staining, to permit analysis and recordation, e.g., as a photograph or a digital or analog scan.
Similarly, nucleic acid analyses utilize a similar gel system, e.g., agarose or polyacrylamide gel. Upon application of a current through the gel, the nucleic acid samples, again disposed in wells at one end (anode) of the gel, will electrophorese through the gel. The polymer gel presents a sieving matrix, where larger nucleic acid fragments that otherwise having the same charge:mass ratio as smaller fragments, will travel more slowly through the gel than the smaller fragments. Upon completion of electrophoresis, the lanes of samples are analyzed for the pattern of the bands (or “ladder” as it is often termed). Analysis of the bands may be carried out by adding a fluorescent intercalating agent to the gel, or by incorporating a radioactive label within the nucleic acid fragments, followed by contacting the gel with a photographic film.
Typically, electrophoresis gels run multiple samples within the same slab gel along with one or more standards or markers, which are used to characterize the sample constituents. For example, in size-based separations, standards typically have a range of known molecular weights. Sample constituents are then compared to the standards to determine their molecular weights, e.g., by interpolation. Such standards must generally be run in the same gel as the sample, in order to provide assurances that the standard was subject to the same separation conditions, e.g., gel composition, electric current, temperature, or other parameters affecting separations.
Despite the efficacy of these slab gel electrophoresis, however, such methods are quickly being supplanted by automated procedures that generate a stream of digital data. This data, in its raw form, may exhibit the non-linearities described earlier, or different ones, or none at all. Such data may be generated, for example, by passing a sample in front of a sensor. Alternatively, it is also possible to digitize the raw information presented in a traditional gel by scanning it to produce a series of measurements. The display of such information is not provided by current systems.
What is therefore needed are techniques for displaying chromatographic separation data that are a series of measurements over time in a format similar to that of traditional gel presentations. Moreover, it would be beneficial to provide normalization of such data, if desired.